Environmental Microbiology of Aquatic and Waste Systems

4.1 Taxonomy of Microorganisms in Aquatic Environments 53

test tube containing the medium; a change in the color

of indicator would indicate acid production by the

organism (see Fig. 4. 7 ).

5. Determination of optimum growth conditions
   Optimum pH, temperature, and oxygen requirements
   are determined by growing the organism under dif­
   ferent conditions of pH and temperature and finding
   the best condition. For oxygen requirement, the
   organism may be grown in an agar stab and sealed
   with sterile molten petroleum jelly to determine if it
   will grow under anaerobic conditions.


6. Secretion of special enzymes
   The secretion of unique enzymes is diagnostic.
   Some of the following enzymes are diagnostic (see
   Fig. 4.7a).

Coagulase: Coagulase is an enzyme produced by

Staphylococcus aureus that converts fibrinogen to

fibrin. In the laboratory, it is used to distinguish

between different types of Staphylococcus isolates.

Coagulase negativity excludes S. aureus. The coagu­

lase test is used to differentiate Staphylococcus

aureus from the other species of Staphylococcus.

The test uses rabbit plasma that has been inoculated

with a staphylococcal colony. The tube is then incu­

bated at 37°C for about 90 min. If positive (i.e., the

suspect colony is S. aureus), the serum will coagu­

late, resulting in a clot. If negative (i.e., if the tested

colony is S. epidermidis), the plasma remains liquid.

Catalase: Catalase is a common enzyme found in

living organisms. Its functions include catalyzing

the decomposition of hydrogen peroxide to water

and oxygen.

Fig. 4.4 Bacterial cell
shapes

Peritrichous

Polar

Fig. 4.5 Bacterial flagellation

Fig. 4.6 Spore locations in the bacterial cell

Bubble of gas in Durham tube

Durham tube

Growth medium with pH indicator

Fig. 4.7 Setup for testing bacterial utilization of various

substrates